U.S. patent application number 15/981714 was filed with the patent office on 2018-09-13 for system and method for a multi-electrode mems device.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Stefan Barzen.
Application Number | 20180262843 15/981714 |
Document ID | / |
Family ID | 57854018 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180262843 |
Kind Code |
A1 |
Barzen; Stefan |
September 13, 2018 |
System and Method for a Multi-Electrode MEMS Device
Abstract
According to an embodiment, a MEMS transducer includes a stator,
a rotor spaced apart from the stator, and a multi-electrode
structure including electrodes with different polarities. The
multi-electrode structure is formed on one of the rotor and the
stator and is configured to generate a repulsive electrostatic
force between the stator and the rotor. Other embodiments include
corresponding systems and apparatus, each configured to perform
corresponding embodiment methods.
Inventors: |
Barzen; Stefan; (Muenchen,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
57854018 |
Appl. No.: |
15/981714 |
Filed: |
May 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14818007 |
Aug 4, 2015 |
10003889 |
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15981714 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04R 2307/027 20130101;
H04R 19/005 20130101; H04R 31/00 20130101; H04R 7/10 20130101; H04R
2307/025 20130101 |
International
Class: |
H04R 19/00 20060101
H04R019/00; H04R 31/00 20060101 H04R031/00 |
Claims
1. A microelectromechanical systems (MEMS) device, the MEMS device
comprising: a deflectable structure; a first structure comprising a
first electrode configured to have a first charge polarity, and a
second electrode configured to have a second charge polarity,
wherein the second charge polarity is different from the first
charge polarity; a second structure comprising a third electrode
configured to have the first charge polarity; and wherein the first
structure is spaced apart from the second structure, and the first
structure and the second structure are configured to vary a
distance between portions of the first structure and the second
structure during deflections of the deflectable structure.
2. The MEMS device of claim 1, wherein the first structure
comprises the deflectable structure and the second structure
comprises a rigid structure.
3. The MEMS device of claim 2, wherein: the MEMS device is an
acoustic transducer; the deflectable structure comprises a
deflectable membrane; and the rigid structure comprises a rigid
perforated backplate.
4. The MEMS device of claim 1, wherein the first structure
comprises a rigid structure and the second structure comprises the
deflectable structure.
5. The MEMS device of claim 4, wherein: the MEMS device is an
acoustic transducer; the rigid structure comprises a rigid
perforated backplate; and the deflectable structure comprises a
deflectable membrane.
6. The MEMS device of claim 1, wherein the first electrode and the
second electrode are configured to: generate a net repulsive
electrostatic force between the first structure and the second
structure when one or more bias voltages are applied to the first
electrode and the second electrode; generate the net repulsive
electrostatic force between the first structure and the second
structure when the first structure and the second structure are
separated by a first distance; and generate a net attractive
electrostatic force between the first structure and the second
structure when the first structure and the second structure are
separated by a second distance that is larger than the first
distance.
7. A method of forming a microelectromechanical systems (MEMS)
device, the method comprising: forming a first structure comprising
a dipole electrode including a first electrode and a second
electrode; forming a structural layer in contact with the first
structure around a circumference of the first structure; and
forming a second structure comprising a third electrode, wherein
the structural layer is in contact with the second structure around
a circumference of the second structure, and the first structure is
spaced apart from the second structure by the structural layer.
8. The method of claim 7, wherein forming the first structure
comprises: forming a first structural layer; forming a plurality of
first electrodes on a top surface of the first structural layer;
and forming a plurality of second electrodes on a bottom surface of
the first structural layer.
9. The method of claim 8, wherein forming the first structural
layer comprises forming a first insulating layer.
10. The method of claim 8, wherein forming the first structural
layer comprises: forming a first conducting layer; forming a first
insulating layer on a top surface of the first conducting layer;
and forming a second insulating layer on a bottom surface of the
first conducting layer.
11. The method of claim 7, wherein forming the first structure
comprises: forming a first structural layer; forming a plurality of
first electrodes on a first surface of the first structural layer;
and forming a plurality of second electrodes on the first surface
of the first structural layer.
12. The method of claim 11, wherein forming the first structural
layer comprises: forming a first conducting layer; and forming a
first insulating layer between the first conducting layer and both
the plurality of first electrodes and the plurality of second
electrodes.
13. The method of claim 12, wherein the plurality of first
electrodes and the plurality of second electrodes are formed on and
in contact with first insulating layer.
14. The method of claim 12, wherein the plurality of second
electrodes are formed overlying the plurality of first electrodes;
and forming the first structure further comprises forming a second
insulating layer between the plurality of first electrodes and the
plurality of second electrodes.
15. A microelectromechanical systems (MEMS) device, the MEMS device
comprising: a deflectable structure; a rigid structure spaced apart
from the deflectable structure; a first structure disposed on one
of the deflectable structure or the rigid structure, the first
structure comprising a first electrode configured to have a first
charge polarity, a second electrode configured to have a second
charge polarity, and wherein the second charge polarity is
different from the first charge polarity; and wherein the first
structure is configured to generate a net repulsive electrostatic
force between the deflectable structure and the rigid structure
when one or more bias voltages are applied to the first structure,
generate the net repulsive electrostatic force between the
deflectable structure and the rigid structure when the deflectable
structure and the rigid structure are separated by a first
distance, and generate a net attractive electrostatic force between
the deflectable structure and the rigid structure when the
deflectable structure and the rigid structure are separated by a
second distance that is larger than the first distance.
16. The MEMS device of claim 15, wherein the first structure is
disposed on the deflectable structure.
17. The MEMS device of claim 15, wherein the first structure is
disposed on the rigid structure.
18. The MEMS device of claim 15, wherein: the MEMS device is an
acoustic transducer; the deflectable structure comprises a
deflectable membrane; and the rigid structure comprises a rigid
perforated backplate.
19. The MEMS device of claim 15, wherein the first electrode and
the second electrode are configured to have a dipole moment that is
substantially perpendicular to a first major surface of the rigid
structure.
20. The MEMS device of claim 15, wherein the first electrode and
the second electrode are separated by an insulating layer and
formed as a layered stack disposed on a first major surface of the
deflectable structure or the rigid structure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of U.S. application Ser.
No. 14/818,007, entitled "System and Method for a Multi-Electrode
MEMS Device," filed on Aug. 4, 2015 which application is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to
microelectromechanical systems (MEMS), and, in particular
embodiments, to a system and method for a multi-electrode MEMS
device.
BACKGROUND
[0003] Transducers convert signals from one domain to another. For
example, some sensors are transducers that convert physical signals
into electrical signals. On the other hand, some transducers
convert electrical signals into physical signals. A common type of
sensor is a pressure sensor that converts pressure differences
and/or pressure changes into electrical signals. Pressure sensors
have numerous applications including, for example, atmospheric
pressure sensing, altitude sensing, and weather monitoring. Another
common type of sensor is a microphone that converts acoustic
signals into electrical signals.
[0004] Microelectromechanical systems (MEMS) based transducers
include a family of transducers produced using micromachining
techniques. MEMS, such as a MEMS pressure sensor or a MEMS
microphone, gather information from the environment by measuring
the change of physical state in the transducer and transferring the
signal to be processed by the electronics, which are connected to
the MEMS sensor. MEMS devices may be manufactured using
micromachining fabrication techniques similar to those used for
integrated circuits.
[0005] MEMS devices may be designed to function as oscillators,
resonators, accelerometers, gyroscopes, pressure sensors,
microphones, microspeakers, and/or micro-mirrors, for example. Many
MEMS devices use capacitive sensing techniques for transducing the
physical phenomenon into electrical signals. In such applications,
the capacitance change in the sensor is converted to a voltage
signal using interface circuits.
[0006] Microphones and microspeakers may also be implemented as
capacitive MEMS devices that include deflectable membranes and
rigid backplates. For a microphone, an acoustic signal as a
pressure difference causes the membrane to deflect. Generally, the
deflection of the membrane causes a change in distance between the
membrane and the backplate, thereby changing the capacitance. Thus,
the microphone measures the acoustic signal and generates an
electrical signal. For a microspeaker, an electrical signal is
applied between the backplate and the membrane at a certain
frequency. The electrical signal causes the membrane to oscillate
at the frequency of the applied electrical signal, which changes
the distance between the backplate and the membrane. As the
membrane oscillates, the deflections of the membrane cause local
pressure changes in the surrounding medium and produce acoustic
signals, i.e., sound waves.
[0007] In MEMS microphones or microspeakers, as well as in other
MEMS devices that include deflectable structures with applied
voltages for sensing or actuation, pull-in or collapse is a common
issue. If a voltage is applied to the backplate and the membrane,
there is a risk of sticking as the membrane and the backplate move
closer together during deflection. This sticking of the two plates
is often referred to as pull-in or collapse and may cause device
failure in some cases. Collapse generally occurs because the
attractive force caused by a voltage difference between the
membrane and the backplate may increase quickly as the distance
between the membrane and the backplate decreases.
SUMMARY
[0008] According to an embodiment, a MEMS transducer includes a
stator, a rotor spaced apart from the stator, and a multi-electrode
structure including electrodes with different polarities. The
multi-electrode structure is formed on one of the rotor and the
stator and is configured to generate a repulsive electrostatic
force between the stator and the rotor. Other embodiments include
corresponding systems and apparatus, each configured to perform
corresponding embodiment methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0010] FIG. 1 illustrates a system block diagram of an embodiment
MEMS transducer system;
[0011] FIGS. 2a and 2b illustrate schematic diagrams of embodiment
multi-electrode elements;
[0012] FIGS. 3a, 3b, 3c, 3d, 3e, and 3f illustrate side-view
schematic diagrams of embodiment multi-electrode transducers;
[0013] FIGS. 4a, 4b, 4c, and 4d illustrate top-view schematic
diagrams of embodiment multi-electrode transducer plates;
[0014] FIG. 5 illustrates a perspective-view cross-section diagram
of an embodiment multi-electrode transducer;
[0015] FIGS. 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, and 6l
illustrate cross sections of embodiment multi-electrode
elements;
[0016] FIGS. 7a, 7b, 7c, 7d, and 7e illustrate cross sections of
embodiment MEMS acoustic transducers;
[0017] FIG. 8 illustrates a block diagram of an embodiment method
of forming a MEMS transducer;
[0018] FIGS. 9a, 9b, and 9c illustrate block diagrams of embodiment
methods of forming multi-electrode elements; and
[0019] FIGS. 10a and 10b illustrate force plots of two
transducers.
[0020] Corresponding numerals and symbols in the different figures
generally refer to corresponding parts unless otherwise indicated.
The figures are drawn to clearly illustrate the relevant aspects of
the embodiments and are not necessarily drawn to scale.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0021] The making and using of various embodiments are discussed in
detail below. It should be appreciated, however, that the various
embodiments described herein are applicable in a wide variety of
specific contexts. The specific embodiments discussed are merely
illustrative of specific ways to make and use various embodiments,
and should not be construed in a limited scope.
[0022] Description is made with respect to various embodiments in a
specific context, namely microphone transducers, and more
particularly, MEMS microphones and MEMS microspeakers. Some of the
various embodiments described herein include MEMS transducer
systems, MEMS microphone systems, dipole electrode MEMS
transducers, multipole electrode MEMS transducers, and fabrications
sequences for various multi-electrode MEMS device. In other
embodiments, aspects may also be applied to other applications
involving any type of transducer that includes a deflectable
structure according to any fashion as known in the art.
[0023] According to various embodiments, MEMS microphones and MEMS
microspeakers include multiple electrodes on the membrane, the
backplate, or both. In such embodiments, separate electrodes are
patterned on one or both of the capacitive plates of the MEMS
acoustic transducer. The separate electrodes and the other
capacitive plate, or other separate electrodes, are supplied with
voltages in order to form an electrostatic field with a dipole or
multipole pattern. In such fields, the membrane and backplate may
be attracted for certain distances and repulsed for other
distances. Thus, various embodiments include MEMS acoustic
transducers capable of applying both attractive and repulsive
electrostatic forces. Such embodiment MEMS acoustic transducers may
operate with higher bias voltages and lower risk of collapse or
pull-in, resulting in improved performance.
[0024] According to various embodiments, multiple types of
multi-electrode structures are formed. Various MEMS acoustic
transducers include single and double backplate MEMS microphones
and MEMS microspeakers. In further embodiments, multi-electrode
structures may be formed in other types of MEMS device that include
deflectable structures, such as pressure sensors, gyroscopes,
oscillators, actuators, and others, for example.
[0025] FIG. 1 illustrates a system block diagram of an embodiment
MEMS transducer system 100 including MEMS transducer 102,
application specific integrated circuit (ASIC) 104, and processor
106. According to various embodiments, MEMS transducer 102
transduces physical signals. In embodiments where MEMS transducer
102 is an actuator, MEMS transducer 102 generates physical signals
by moving a deflectable structure based on excitation from
electrical signals. In embodiments where MEMS transducer 102 is a
sensor, MEMS transducer 102 generates electrical signals by
transducing physical signals that cause the deflectable structure
to move and generate the electrical signals. In the various
embodiments, MEMS transducer 102 includes a multi-electrode
deflectable structure that produces a dipole type electric field or
a multipole electric field as described further herein below.
[0026] In various embodiments, MEMS transducer 102 may be a MEMS
microphone. In other embodiments, MEMS transducer 102 may be a MEMS
microspeaker. In some applications, MEMS transducer 102 may be a
MEMS acoustic transducer that both senses and actuates acoustic
signals. For example, MEMS transducer 102 may be a combination
acoustic sensor and actuator for high frequency applications, such
as ultrasound transducers. In some embodiments, capacitive MEMS
microphones may include a membrane and backplate with smaller
surface areas and separation distances than typically found in
capacitive MEMS microspeakers.
[0027] In various embodiments, ASIC 104 either generates the
electrical signals for exciting MEMS transducer 102 or receives the
electrical signals generated by MEMS transducer 102. ASIC 104 may
also provide voltage bias or voltage drive signals to MEMS
transducer 102 depending on various applications. In some
embodiments, ASIC 104 includes an analog to digital converter (ADC)
or a digital to analog converter (DAC). Processor 106 interfaces
with ASIC 104 and generates drive signals or provides signal
processing. Processor 106 may be a dedicated transducer processor,
such as a CODEC for a MEMS microphone, or may be a general
processor, such as a microprocessor.
[0028] FIGS. 2a and 2b illustrate schematic diagrams of embodiment
multi-electrode elements 110 and 111. FIG. 2a illustrates
multi-electrode element 110, which includes dipole electrode 114
and electrode 112. According to various embodiments, dipole
electrode 114 may be formed on a backplate in a MEMS microphone,
for example, and electrode 112 may be a membrane in the MEMS
microphone. Dipole electrode 114 includes a pole with a positive
polarity and a pole with a negative polarity. In such embodiments,
the positive and negative polarities are electrical potentials
relative to each other. Thus, the positive and negative polarities
may include two different positive voltages with respect to ground,
two different negative voltages with respect to ground, or a
positive and a negative voltage with respect to ground. Electrode
112 and dipole electrode 114 are driven with voltages to produce
the electric field as shown (where the electric field lines are not
necessarily drawn to scale). As illustrated, electrode 112 is
indicated with a negative polarity. When electrode 112 is beyond a
certain distance from dipole electrode 114, the electrostatic force
acting between electrode 112 and dipole electrode 114 may be
attractive. When electrode 112 is within the certain distance from
dipole electrode 114, the electrostatic force acting between
electrode 112 and dipole electrode 114 may be repulsive. Thus, as
the membrane, with electrode 112, moves towards the backplate, with
dipole electrode 114, the electrostatic force acting on the
membrane is attractive initially and may become repulsive within a
certain separation distance. Thus, in various embodiments,
electrostatic repulsive forces may be used between the backplate
and the membrane to prevent collapse or pull-in.
[0029] In other embodiments, dipole electrode 114 may be arranged
on the membrane and electrode 112 may be arranged on the backplate.
Further, an additional backplate may be included with either
configuration. In further embodiments, dipole electrode 114 and
electrode 112 may be included in any type of MEMS device with
movable structure that have applied voltages or include electrodes,
for example.
[0030] According to various embodiments, both the membrane and the
backplate may include dipole electrodes or, more generally, both
the fixed structure and the deflectable structure of a MEMS device
may include dipole electrodes. FIG. 2b illustrates multi-electrode
element 111, which includes dipole electrode 116 and dipole
electrode 118. According to such embodiments, dipole electrode 116
is arranged on the membrane of a MEMS microphone and dipole
electrode 118 is arranged on the backplate of the MEMS microphone.
As described hereinabove in reference to FIG. 2a, depending on the
voltages applied to, and the separation distance between, dipole
electrode 116 and dipole electrode 118, the electrostatic forces
acting on both dipoles may be arranged to be attractive or
repulsive. Dipole electrode 116 and dipole electrode 118 each have
a pole with a negative polarity and a pole with a positive
polarity, which may include different positive or negative voltages
with respect to ground. In such embodiments, multi-electrode
element 111 may be referred to as a quadrupole. In various further
embodiments, any number of electrodes, including dipole electrodes,
may be patterned on a membrane or a backplate for a MEMS acoustic
transducer, as described further herein below. In other
embodiments, any number of electrodes, including dipole electrodes,
may be patterned on movable or fixed structures in a MEMS
device.
[0031] FIGS. 3a, 3b, 3c, 3d, 3e, and 3f illustrate side-view
schematic diagrams of embodiment multi-electrode transducers 120a,
120b, 120c, 120d, 120e, and 120f. FIG. 3a illustrates
multi-electrode transducer 120a including isolating plate 122,
conductive plate 124, and dipole electrodes 126 on isolating plate
122. According to various embodiments, each of dipole electrodes
126 operates with conductive plate 124 as described hereinabove in
reference to FIG. 2a. Isolating plate 122 is the membrane of a MEMS
acoustic transducer and conductive plate 124 is the backplate of
the MEMS acoustic transducer in some embodiments. In other
embodiments, isolating plate 122 is the backplate of the MEMS
acoustic transducer and conductive plate 124 is the membrane of the
MEMS acoustic transducer. In various embodiments, the membrane
(either conductive plate 124 or isolating plate 122) may experience
an attractive force for some separation distances and a repulsive
force for other separation distances depending on the electric
fields formed by conductive plate 124 and dipole electrodes
126.
[0032] According to various embodiments, each dipole electrode 126
is formed with a positive pole on a top surface of isolating plate
122 and a negative pole on a bottom surface of isolating plate 122.
Isolating plate 122 may be an insulator in some embodiments. In
alternative embodiments, isolating plate 122 may include a
conductor, or conductors, with insulating layers formed on the top
or bottom surfaces of the conductor, or conductors. In other
embodiments, the positive pole of each dipole electrode 126 is
formed on the bottom surface of isolating plate 122 and the
negative pole of each dipole electrode 126 is formed on the top
surface of isolating plate 122 (opposite as shown).
[0033] FIG. 3b illustrates multi-electrode transducer 120b
including isolating plate 122, conductive plate 124, and dipole
electrodes 128 on isolating plate 122. According to various
embodiments, multi-electrode transducer 120b operates as similarly
described hereinabove in reference to multi-electrode transducer
120a, with the exception that dipole electrodes 128 each include a
positive pole and negative pole formed on a same side of isolating
plate 122. Dipole electrodes 128 operate with conductive plate 124
as described hereinabove in reference to FIG. 2a. In such
embodiments, the positive and negative poles of dipole electrodes
128 may be separated by some insulating material (not shown).
Further, isolating plate 122 is an insulator in various
embodiments. In alternative embodiments, isolating plate 122 may
include a conductor with isolating layers formed on the top or
bottom surfaces of the conductor. In such embodiments, dipole
electrodes 128 may still be isolated from each other by isolating
plate 122. In various embodiments, dipole electrodes 128 may be
formed on either the top or bottom sides of isolating plate
122.
[0034] According to various embodiments, isolating plate 122 is the
membrane of the MEMS acoustic transducer and conductive plate 124
is the backplate of the MEMS acoustic transducer in some
embodiments. In other embodiments, isolating plate 122 is the
backplate of the MEMS acoustic transducer and conductive plate 124
is the membrane of the MEMS acoustic transducer. In various
embodiments, the membrane (either conductive plate 124 or isolating
plate 122) may experience an attractive force for some separation
distances and a repulsive force for other separation distances
depending on the electric fields formed by conductive plate 124 and
dipole electrodes 128.
[0035] FIG. 3c illustrates multi-electrode transducer 120c
including isolating plate 122, isolating plate 132, dipole
electrodes 130 on isolating plate 122, and dipole electrodes 134 on
isolating plate 132. According to various embodiments, dipole
electrodes 128 and dipole electrodes 134 operate as described
hereinabove in reference to FIG. 2b. In such embodiments, each of
dipole electrodes 130 and dipole electrodes 134 includes a positive
pole and a negative pole. Each of dipole electrodes 130 is formed
on isolating plate 122 in line with a corresponding one of dipole
electrodes 134 formed on isolating plate 132. For each dipole of
dipole electrodes 130 and dipole electrodes 134, the axis, from
negative to positive poles, of the corresponding dipoles are
arranged in parallel to each other and perpendicular to the
separation distance between the corresponding dipoles.
[0036] According to various embodiments, isolating plate 122 and
isolating plate 132 are insulators. In alternative embodiments,
isolating plate 122 and isolating plate 132 may include conductors
with isolating layers formed on the top or bottom surfaces of the
conductors. In such embodiments, dipole electrodes 130 and dipole
electrodes 134 may still be isolated from each other by isolating
plate 122 and isolating plate 132, respectively. In various
embodiments, dipole electrodes 130 and dipole electrodes 134 may be
formed on either the top or bottom sides of isolating plate 122 and
isolating plate 132, respectively. Each corresponding pair of
dipoles from dipole electrodes 130 and dipole electrodes 134 may be
referred to as a quadrupole, as described hereinabove in reference
to FIG. 2b.
[0037] According to various embodiments, isolating plate 122 is the
membrane of the MEMS acoustic transducer and isolating plate 132 is
the backplate of the MEMS acoustic transducer. In other
embodiments, isolating plate 122 is the backplate of the MEMS
acoustic transducer and isolating plate 132 is the membrane of the
MEMS acoustic transducer. In various embodiments, the membrane
(either isolating plate 132 or isolating plate 122) may experience
an attractive force for some separation distances and a repulsive
force for other separation distances depending on the electric
fields formed by dipole electrodes 130 and dipole electrodes
134.
[0038] FIG. 3d illustrates multi-electrode transducer 120d
including isolating plate 122, conductive plate 124, and electrodes
136. According to various embodiments, electrodes 136 may be
connected together or be connected to separate charge sources.
Electrodes 136 may include charges with a first polarity near the
center and charges with a second polarity, opposite the first
polarity, near the periphery. The charge distribution may be
attained by a discontinuous distribution of electrodes with a
definite amount of charge present on electrodes 136, such as
described further herein below in reference to FIG. 4c. In various
embodiments, conductive plate 124 and electrodes 136 operate in a
similar manner as described hereinabove in reference to FIGS. 2a
and 2b. In such embodiments, for some separation distances, an
attractive force exists between conductive plate 124 and isolating
plate 122 with electrodes 136. For other separation distances, a
repulsive force exists between conductive plate 124 and isolating
plate 122 with electrodes 136.
[0039] According to various embodiments, electrodes 136 may be
formed on a top surface or a bottom surface of isolating plate 122.
Isolating plate 122 is the membrane of the MEMS acoustic transducer
and conductive plate 124 is the backplate of the MEMS acoustic
transducer in some embodiments. In other embodiments, isolating
plate 122 is the backplate of the MEMS acoustic transducer and
conductive plate 124 is the membrane of the MEMS acoustic
transducer. In various embodiments, the membrane (either isolating
plate 122 or conductive plate 124) may experience an attractive
force for some separation distances and a repulsive force for other
separation distances depending on the electric fields formed by
electrodes 136 and conductive plate 124.
[0040] FIG. 3e illustrates multi-electrode transducer 120e
including isolating plate 122, isolating plate 132, dipole
electrodes 126 on isolating plate 122, and dipole electrodes 138 on
isolating plate 132. According to various embodiments, each of
dipole electrodes 126 operates with a corresponding one of dipole
electrodes 138 to function in a similar manner as described
hereinabove in reference to multi-electrode element 110 and
multi-electrode element 111 in FIGS. 2a and 2b. Isolating plate 122
is the membrane of the MEMS acoustic transducer and isolating plate
132 is the backplate of the MEMS acoustic transducer in some
embodiments. In other embodiments, isolating plate 122 is the
backplate of the MEMS acoustic transducer and isolating plate 132
is the membrane of the MEMS acoustic transducer. In various
embodiments, the membrane (either isolating plate 122 or isolating
plate 132) may experience an attractive force for some separation
distances and a repulsive force for other separation distances
depending on the electric fields formed by dipole electrodes 126
and dipole electrodes 138.
[0041] According to various embodiments, each dipole electrode 126
is formed with a positive pole on a top surface of isolating plate
122 and a negative pole on a bottom surface of isolating plate 122.
Similarly, each dipole electrode 138 is formed with a positive pole
on a bottom surface of isolating plate 132 and a negative pole on a
top surface of isolating plate 132. Isolating plate 122 and
isolating plate 132 may each be an insulator in some embodiments.
In other embodiments, isolating plate 122 and isolating plate 132
may each be a conductor with insulating layers formed on the top
and bottom surfaces. In alternative embodiments, the positive pole
of each dipole electrode 126 is formed on the bottom surface of
isolating plate 122 and the negative pole of each dipole electrode
126 is formed on the top surface of isolating plate 122 (opposite
as shown), while the positive pole of each dipole electrode 138 is
formed on the top surface of isolating plate 132 and the negative
pole of each dipole electrode 138 is formed on the bottom surface
of isolating plate 132 (opposite as shown).
[0042] FIG. 3f illustrates multi-electrode transducer 120f
including isolating plate 122, isolating plate 132, dipole
electrodes 128 on isolating plate 122, and dipole electrodes 140 on
isolating plate 132. According to various embodiments,
multi-electrode transducer 120f operates as similarly described
hereinabove in reference to multi-electrode transducer 120e, with
the exception that dipole electrodes 128 and dipole electrodes 140
each include a positive pole and negative pole formed on a same
side of isolating plate 122 or isolating plate 132, respectively.
Dipole electrodes 128 operate with dipole electrodes 140 as
described hereinabove in reference to multi-electrode transducer
120e in FIG. 3e. In such embodiments, the positive and negative
poles of dipole electrodes 128 and dipole electrodes 140 may be
separated by some insulating material (not shown). In various
embodiments, dipole electrodes 128 and dipole electrodes 140 may be
formed on either the top or bottom sides of isolating plate 122 or
isolating plate 132, respectively.
[0043] According to various embodiments, isolating plate 122 is the
membrane of the MEMS acoustic transducer and isolating plate 132 is
the backplate of the MEMS acoustic transducer in some embodiments.
In other embodiments, isolating plate 122 is the backplate of the
MEMS acoustic transducer and isolating plate 132 is the membrane of
the MEMS acoustic transducer. In various embodiments, the membrane
(either isolating plate 132 or isolating plate 122) may experience
an attractive force for some separation distances and a repulsive
force for other separation distances depending on the electric
fields formed by dipole electrodes 140 and dipole electrodes
128.
[0044] FIGS. 3a, 3b, 3c, 3d, 3e, and 3f illustrate multi-electrode
transducers 120a, 120b, 120c, 120d, 120e, and 120f according to
various embodiments. The various electrodes depicted, such as
dipole electrodes 126, dipole electrodes 128, dipole electrodes
130, dipole electrodes 134, and electrodes 136, may be included in
embodiments with any number of dipole electrodes. That is, in the
various figures, four or eight dipole electrodes, for example, are
illustrated; however, any number of dipole electrodes or electrodes
may be included on a conductive or isolating plate for a membrane
or backplate in various embodiments. Similarly, in various other
embodiments that include structures without a membrane or
backplate, any number of dipole electrodes or electrodes may be
included.
[0045] FIGS. 4a, 4b, 4c, and 4d illustrate top-view schematic
diagrams of embodiment multi-electrode transducer plates 150a,
150b, and 150c. FIG. 4a illustrates a top view of multi-electrode
transducer plate 150a, which may be part of one implementation of
multi-electrode transducer 120c described hereinabove in reference
to FIG. 3c. According to various embodiments, multi-electrode
transducer plate 150a includes first electrodes 154, second
electrodes 156, isolating plate 152, connection 158, and connection
160. First electrodes 154 and second electrodes 156 are formed on a
top or bottom surface of isolating plate 152 in a circular pattern.
In such embodiments, isolating plate 152 may be a backplate or a
membrane and may include an additional plate, such as an isolating
plate or a conductive plate as described hereinabove in reference
to FIGS. 3a-3f, formed beneath isolating plate 152. In other
embodiments, isolating plate 152 is another shape, such as
rectangular or oval. In various embodiments, first electrodes 154
and second electrodes 156 may be formed on a top or bottom surface
of isolating plate 152 in an oval or rectangular pattern. The
additional plate may have similar or identical structures as
multi-electrode transducer plate 150a or may include a conductive
plate for example. In various embodiments, isolating plate 152 is
one implementation of isolating plate 122 and is an insulator. In
alternative embodiments, isolating plate 152 may include a
conductor, or conductors, with isolating layers formed on the top
or bottom surfaces of the conductor, or conductors.
[0046] According to various embodiments, connection 158 couples
first electrodes 154 to a first charge source and connection 160
couples second electrodes 156 to a second charge source. In such
embodiments, adjacent electrodes of first electrodes 154 and second
electrodes 156 form positive and negative poles of dipole
electrodes. In one embodiment, as similarly illustrated in FIG. 3c,
connection 158 provides charge for positive poles of each dipole
electrode and connection 160 provides charge for negative poles of
each dipole electrode. In various embodiments, connection 160 and
connection 158 are formed opposite one another as shown. In other
embodiments, connection 160 and connection 158 may be formed with
any orientation and may be formed overlying one another.
[0047] FIG. 4b illustrates a top view of multi-electrode transducer
plate 150b, which may be part of one implementation of
multi-electrode transducers 120a, 120b, 120e, or 120f described
hereinabove in reference to FIGS. 3a, 3b, 3e, and 3f. According to
various embodiments, multi-electrode transducer plate 150b includes
electrodes 162, isolating plate 152, connection 166, and connection
166. Electrodes 162 are formed on a top surface of isolating plate
152 in a circular pattern. Connection 164 couples each of
electrodes 162 to a common charge source.
[0048] In various embodiments, additional electrodes may be
included beneath electrodes 162 or beneath isolation plate 152. In
such embodiments, connection 166 is coupled to the additional
electrodes. In one embodiment, as described hereinabove in
reference to FIG. 3a, electrodes 162 coupled to connection 164 may
form the positive poles on a top surface of isolating plate 152 and
additional electrodes coupled to connection 166 may form the
negative poles on a bottom surface of isolating plate 152 for
dipole electrodes. In another embodiment, as described hereinabove
in reference to FIG. 3b, electrodes 162 coupled to connection 164
may form the negative poles on the top surface of isolating plate
152 and additional electrodes coupled to connection 166 may form
the positive poles beneath the negative poles on the top surface of
isolating plate 152 for dipole electrodes.
[0049] According to various embodiments, as described in reference
to FIGS. 3a, 3b, 3e, and 3f, an additional plate may be formed
beneath isolating plate 152 in multi-electrode transducer plate
150b. The additional plate may include a conductive plate in some
embodiments, as described in reference to FIGS. 3a and 3b. The
additional plate may include an isolating plate in other
embodiments, as described in reference to FIGS. 3e and 3f. In
various embodiments, the additional plate may include similar or
identical structures as multi-electrode transducer plate 150b. In
various embodiments, connection 164 and connection 166 are formed
opposite one another as shown. In other embodiments, connection 164
and connection 166 may be formed with any orientation and may be
formed overlying one another.
[0050] FIG. 4c illustrates a top view of multi-electrode transducer
plate 150c, which may be part of one implementation of
multi-electrode transducer 120d described hereinabove in reference
to FIG. 3d. According to various embodiments, multi-electrode
transducer plate 150c includes isolating plate 152, electrode 168,
and connection 158. Electrode 168 includes circular electrode rings
formed on isolating plate 152 with breaks or discontinuities near a
straight portion extending radially as connection 158. In such
embodiments, the structure of electrode 168 may cause charges to
distribute around electrode 168 as described in reference to
electrode 136 in FIG. 3d. An additional plate may be formed beneath
isolating plate 152 in multi-electrode transducer plate 150c. The
additional plate may include a conductive plate in some
embodiments, as described in reference to FIG. 3d. In an
alternative embodiment, the additional plate may include an
isolating plate that may have patterned electrodes.
[0051] FIG. 4d illustrates a top view of multi-electrode transducer
plate 150d, which may be part of one implementation of
multi-electrode transducer 120c described hereinabove in reference
to FIG. 3c. According to various embodiments, multi-electrode
transducer plate 150d includes first electrodes 154, second
electrodes 156, isolating plate 152, connection 158, and connection
160, as described hereinabove in reference to FIG. 4a.
Multi-electrode transducer plate 150d is similar to multi-electrode
transducer plate 150a, with the exception that first electrodes 154
and second electrodes 156 may include a gap, e.g., a break or
discontinuity, at connection 160 and connection 158, respectively.
In such embodiments, first electrodes 154, second electrodes 156,
connection 158, and connection 160 may be patterned using a single
mask. In other embodiments, one or more additional layers may be
formed at the gap or gaps in first electrodes 154 or second
electrodes 156.
[0052] FIG. 5 illustrates a perspective-view cross-section diagram
of an embodiment multi-electrode transducer 170, which may be one
implementation of multi-electrode transducer 120c described
hereinabove in reference to FIG. 3c. According to various
embodiments, multi-electrode transducer 170 includes top plate 171,
bottom plate 172, electrodes 174, and electrodes 176. Top plate 171
may be a backplate for an acoustic MEMS transducer and bottom plate
172 may be a membrane of the acoustic MEMS transducer. Top plate
171 is perforated with perforations 178 in some embodiments. As
shown and similarly described hereinabove in reference to
multi-electrode transducer 120c in FIG. 3c, electrodes 174 include
alternating charge polarities and electrodes 176 also include
alternating charge polarities.
[0053] Top plate 171 and bottom plate 172 may be insulators with
patterned electrodes 174 and 176, respectively. In other
embodiments, top plate 171 and bottom plate 172 may be conductors
with insulating layers formed on top or bottom surfaces of top
plate 171 or bottom plate 172. Further, electrodes 174 and 176 may
be formed on top or bottom surfaces of top plate 171 or bottom
plate 172. In other embodiments, top plate 171 or bottom plate 172
may include any type of electrode configuration described
hereinabove in reference to FIGS. 3a-3f and 4a-4d.
[0054] In reference to FIGS. 3a-3f, 4a-4d, and 5, description is
made with reference to directions such as below or above, top or
bottom. One of ordinary skill in the art will recognize that these
configurations may be swapped in some embodiments. Further, the
various electrode and plate configurations may be arranged as a
membrane, backplate, or both in some embodiments for a MEMS
acoustic transducer. The description and figures depict general
electrode configurations diagrammatically without showing specific
detail as to semiconductor structures for implementing the depicted
electrode configurations. Various embodiment semiconductor
structures for implementing the various embodiment electrode
configurations are described further herein below in reference to
the other figures.
[0055] FIGS. 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, and 6l
illustrate cross sections of embodiment multi-electrode elements
200a, 200b, 200c, 200d, 200e, 200f, 200g, and 200h. According to
various embodiments, multi-electrode elements 200a-200h include
device layers and structures for forming various electrodes and
dipole electrodes for embodiment multi-electrode transducers as
described hereinabove in reference to the other figures. FIGS.
6a-6l illustrate portions of various embodiment electrodes and
dipole electrodes. The same device layers and patterning may be
applied to form any number of electrodes for embodiment
multi-electrode transducers.
[0056] FIG. 6a illustrates multi-electrode element 200a including
insulating layer 202, first electrodes 204, and second electrodes
206. In various embodiments, insulating layer 202 is formed of
silicon nitride or silicon dioxide. In further embodiments,
insulating layer 202 may be formed of any type of oxide or nitride.
Insulating layer 202 may be any type of insulator suitable for
fabrication and operation with embodiment multi-electrode
transducers, such as a polymer in alternative embodiments.
[0057] First electrodes 204 may be formed as a common conductive
layer and patterned. First electrodes 204 are formed of polysilicon
in one embodiment. First electrodes 204 are formed of metal in
other embodiments. In such embodiments, first electrodes 204 are
formed of aluminum, silver, or gold. In other embodiments, first
electrodes 204 are formed of any conductor suitable for fabrication
and operation with embodiment multi-electrode transducers, such as
other metals or doped semiconductors.
[0058] Similar to first electrodes 204, second electrodes 206 may
be formed as a common conductive layer and patterned. Second
electrodes 206 are formed of polysilicon in one embodiment. Second
electrodes 206 are formed of metal in other embodiments. In such
embodiments, second electrodes 206 are formed of aluminum, silver,
or gold. In other embodiments, second electrodes 206 are formed of
any conductor suitable for fabrication and operation with
embodiment multi-electrode transducers, such as other metals or
doped semiconductors. In some other embodiments, electrodes, such
as first electrode 204 or second electrode 206, may be included
only on the top surface or only on the bottom surface of the
supporting layer, such as insulating layer 202, instead of on both
the top and bottom surfaces as shown.
[0059] FIG. 6b illustrates multi-electrode element 200a at another
cross-section including insulating layer 202, first electrodes 204,
second electrode 206, first electrical connections 208, and second
electrical connections 210. According to various embodiments, first
electrical connections 208 and first electrodes 204 may be formed
as a common conductive layer and patterned. Thus, first electrical
connections 208 may be any of the materials described in reference
to first electrode 204. Similarly, second electrical connections
210 and second electrodes 206 may be formed as a common conductive
layer and patterned. Thus, second electrical connections 210 may be
any of the materials described in reference to second electrode
206. First electrical connections 208 and second electrical
connections 210 form connections between the various electrodes,
such as first electrodes 204 or second electrodes 206, and may form
connections 164 or 166 as described hereinabove in reference to
FIG. 4b, for example.
[0060] FIG. 6c illustrates multi-electrode element 200b including
conductive layer 212, bottom insulating layer 214, top insulating
layer 216, first electrodes 204, and second electrodes 206. In
various embodiments, bottom insulating layer 214 and top insulating
layer 216 are formed of silicon nitride or silicon dioxide. In
further embodiments, bottom insulating layer 214 and top insulating
layer 216 may be formed of any type of oxide or nitride. Bottom
insulating layer 214 and top insulating layer 216 may be formed of
any type of insulator suitable for fabrication and operation with
embodiment multi-electrode transducers, such as a polymer in
alternative embodiments. First electrodes 204 and second electrodes
206 are formed as described hereinabove in reference to FIGS. 6a
and 6b. In various embodiments, conductive layer 212 may be
patterned with various patterns and structures in order to shape
the electric field formed around multi-electrode elements. In some
specific embodiments, conductive layer 212 may shield the electric
field from crossing conductive layer 212 by terminating the
electric field at conductive layer 212.
[0061] FIG. 6d illustrates multi-electrode element 200b at another
cross-section including conductive layer 212, bottom insulating
layer 214, top insulating layer 216, first electrodes 204, second
electrodes 206, first electrical connections 208, and second
electrical connections 210. According to various embodiments, first
electrical connections 208 and second electrical connections 210
are formed as described hereinabove in reference to FIGS. 6a and
6b. First electrical connections 208 and second electrical
connections 210 form connections between the various electrodes,
such as first electrodes 204 or second electrodes 206, and may form
connections 164 or 166 as described hereinabove in reference to
FIG. 4b, for example.
[0062] FIG. 6e illustrates multi-electrode element 200c including
conductive layer 212, bottom insulating layer 214, top insulating
layer 216, second electrodes 206, electrode insulating layer 218,
and third electrodes 220. In various embodiments, conductive layer
212, bottom insulating layer 214, top insulating layer 216, and
second electrodes 206 are formed as described hereinabove in
reference to FIGS. 6a, 6b, 6c, and 6d. Electrode insulating layer
218 is formed as a layer and patterned on top of second electrodes
206. Electrode insulating layer 218 is formed of silicon nitride or
silicon dioxide. In further embodiments, electrode insulating layer
218 may be formed of any type of oxide or nitride. Electrode
insulating layer 218 may be formed of any type of insulator
suitable for fabrication and operation with embodiment
multi-electrode transducers, such as a polymer in alternative
embodiments.
[0063] Third electrodes 220 may be formed as a common conductive
layer and patterned on top of electrode insulating layer 218. Third
electrodes 220 are formed of polysilicon in one embodiment. Third
electrodes 220 are formed of metal in other embodiments. In such
embodiments, third electrodes 220 are formed of aluminum, silver,
or gold. In other embodiments, third electrodes 220 are formed of
any conductor suitable for fabrication and operation with
embodiment multi-electrode transducers, such as other metals or
doped semiconductors. In some embodiments, bottom insulating layer
214 may be omitted.
[0064] FIG. 6f illustrates multi-electrode element 200c at another
cross-section including conductive layer 212, bottom insulating
layer 214, top insulating layer 216, second electrodes 206, second
electrical connections 210, electrode insulating layer 218,
connection insulating layer 222, third electrodes 220, and third
electrical connections 224. According to various embodiments,
second electrical connections 210 are formed as described
hereinabove in reference to FIGS. 6a and 6b. Third electrical
connections 224 may be formed as a common conductive layer with
third electrodes 220 and patterned. Thus, third electrical
connections 224 may be any of the materials described in reference
to third electrode 220. Connection insulating layer 222 may be
formed as a common insulating layer with electrode insulating layer
218 and patterned. Thus, connection insulating layer 222 may be any
of the materials described in reference to electrode insulating
layer 218.
[0065] According to various embodiments, second electrical
connections 210 and third electrical connections 224 form
connections between the various electrodes, such as second
electrodes 206 or third electrodes 220, and may form connections
164 or 166 as described hereinabove in reference to FIG. 4b, for
example. Connection insulating layer 222 provides insulation
between second electrical connections 210 and third electrical
connections 224. In some embodiments, bottom insulating layer 214
may be omitted.
[0066] FIG. 6g illustrates multi-electrode element 200d at a
cross-section including conductive layer 212, bottom insulating
layer 214, top insulating layer 216, second electrodes 206, second
electrical connections 210, electrode insulating layer 218,
connection insulating layer 222, third electrodes 220, and third
electrical connections 224. Multi-electrode element 200d is similar
to multi-electrode element 200c as described hereinabove in
reference to FIG. 6f with the exception that second electrical
connections 210 and third electrical connections 224 have been
thinned compared to second electrodes 206 and third electrodes 220.
In some embodiments, thinning the connection layers may require an
additional photolithography and mask sequence. Other than the
thinning step, conductive layer 212, bottom insulating layer 214,
top insulating layer 216, second electrodes 206, second electrical
connections 210, electrode insulating layer 218, connection
insulating layer 222, third electrodes 220, and third electrical
connections 224 are formed as described hereinabove in reference to
FIGS. 6a-6f. In some embodiments, bottom insulating layer 214 may
be omitted.
[0067] FIG. 6h illustrates multi-electrode element 200e including
conductive layer 226, insulating layer 228, and conductive layer
230. According to various embodiments, multi-electrode element 200e
is an alternative embodiment that includes thick top and bottom
electrodes formed by conductive layer 226 and conductive layer 230
with thinner insulating layer 228 formed between the conductive
layer 226 and conductive layer 230. In such embodiments, conductive
layer 226, insulating layer 228, and conductive layer 230 may form
a backplate or a membrane. Further, conductive layer 226 and
conductive layer 230 may be patterned to form electrical
connections or electrodes on various portions of the membrane or
backplate.
[0068] Conductive layer 226 may be formed as a common conductive
layer and patterned. Conductive layer 226 is formed of polysilicon
in one embodiment. Conductive layer 226 is formed of metal in other
embodiments. In such embodiments, conductive layer 226 is formed of
aluminum, silver, or gold. In other embodiments, conductive layer
226 is formed of any conductor suitable for fabrication and
operation with embodiment multi-electrode transducers, such as
other metals or doped semiconductors.
[0069] Similar to conductive layer 226, conductive layer 230 may be
formed as a common conductive layer and patterned. Conductive layer
230 is formed of polysilicon in one embodiment. Conductive layer
230 is formed of metal in other embodiments. In such embodiments,
conductive layer 230 is formed of aluminum, silver, or gold. In
other embodiments, conductive layer 230 is formed of any conductor
suitable for fabrication and operation with embodiment
multi-electrode transducers, such as other metals or doped
semiconductors.
[0070] Insulating layer 228 is formed as a layer and patterned
between conductive layer 226 and conductive layer 230. Insulating
layer 228 is formed of silicon nitride or silicon dioxide. In
further embodiments, insulating layer 228 may be formed of any type
of oxide or nitride. Insulating layer 228 may be formed of any type
of insulator suitable for fabrication and operation with embodiment
multi-electrode transducers, such as a polymer in alternative
embodiments.
[0071] FIG. 6i illustrates multi-electrode element 200f including
insulating layer 202, second electrodes 206, electrode insulating
layer 218, and third electrodes 220. In various embodiments,
insulating layer 202, second electrodes 206, electrode insulating
layer 218, and third electrodes 220 are formed as described
hereinabove in reference to FIGS. 6a-6h. Second electrodes 206,
electrode insulating layer 218, and third electrodes 220 are
patterned as described in reference to FIG. 6e.
[0072] FIG. 6j illustrates multi-electrode element 200f at another
cross-section including insulating layer 202, second electrodes
206, second electrical connections 210, electrode insulating layer
218, connection insulating layer 222, third electrodes 220, and
third electrical connections 224. According to various embodiments,
second electrical connections 210, third electrical connections
224, and connection insulating layer 222 are formed as described
hereinabove in reference to FIGS. 6a-6h.
[0073] FIG. 6k and FIG. 6l illustrate multi-electrode elements 200g
and 200h at cross-sections showing electrical connections between
electrodes according to two implementations of multi-electrode
transducer plate 150a as described hereinabove in reference to FIG.
4a. According to various embodiments, second electrodes 206 and
third electrodes 220 may be arranged to alternate polarity, such as
described hereinabove in reference to FIGS. 3c and 4a. Thus, FIGS.
6k and 6l depict electrical connections provided for second
electrodes 206 and third electrodes 220 with alternating polarity.
In such embodiments, insulating layer 202, second electrodes 206,
third electrodes 220, conductive layer 212, bottom insulating layer
214, top insulating layer 216, second electrical connections 210,
connection insulating layer 222, and third electrical connections
224 are formed as described hereinabove in reference to FIGS.
6a-6j. In such embodiments, second electrical connections 210 and
third electrical connections 224 may be thinner or may have a same
thickness as second electrodes 206 or third electrodes 220, as
described hereinabove in reference to FIGS. 6f and 6g, for example.
In some embodiments, bottom insulating layer 214 may be
omitted.
[0074] In various embodiments as described hereinabove in reference
to FIGS. 6a-6l, the various electrodes may be formed on top or
bottom surfaces of the respective supporting surface.
[0075] FIGS. 7a, 7b, 7c, 7d, and 7e illustrate cross sections of
embodiment MEMS acoustic transducers 231a, 231b, 231c, 231d, and
231e. FIGS. 7a, 7b, 7c, 7d, and 7e describe MEMS acoustic
transducers according to specific embodiments for backplates and
membranes. In further embodiments, any of the transducer plate and
electrode embodiments described hereinabove in reference to FIGS.
3a-3f, 4a-4d, 5, and 6a-6l may be included as either backplate,
membrane, or both in the embodiments described in reference to
FIGS. 7a, 7b, 7c, 7d, and 7e. Those skilled in the art will readily
appreciate that the structures and methods described herein in
reference to the various embodiments may be combined or
incorporated in numerous types of MEMS acoustic transducers, as
well as other types of transducers.
[0076] FIG. 7a illustrates MEMS acoustic transducer 231a including
a single backplate 238 and membrane 240. According to various
embodiments, MEMS acoustic transducer 231a includes substrate 232,
isolation 234, structural layer 236, backplate 238, membrane 240,
metallization 254, metallization 256, metallization 258, and
metallization 260. Substrate 232 includes cavity 233 formed below
released portions of membrane 240 and backplate 238.
[0077] In various embodiments, membrane 240 is formed of conductive
layer 244, insulating layer 246, and conductive layer 248. In
various embodiments, insulating layer 246 is formed of silicon
nitride or silicon dioxide. In further embodiments, insulating
layer 246 may be formed of any type of oxide or nitride. Insulating
layer 246 may be any type of insulator suitable for fabrication and
operation with embodiment multi-electrode transducers, such as a
polymer in alternative embodiments.
[0078] Conductive layer 244 and conductive layer 248 may be formed
as conductive layers on the top and bottom surfaces of insulating
layer 246, respectively. Further, conductive layer 244 and
conductive layer 248 are patterned to form dipole electrodes 250
and electrical connections 252. Conductive layer 244 and conductive
layer 248 are formed of polysilicon in one embodiment. Conductive
layer 244 and conductive layer 248 are formed of metal in other
embodiments. In such embodiments, conductive layer 244 and
conductive layer 248 are formed of aluminum, silver, or gold. In
other embodiments, conductive layer 244 and conductive layer 248
are formed of any conductor suitable for fabrication and operation
with embodiment multi-electrode transducers, such as other metals
or doped semiconductors.
[0079] In various embodiments, backplate 238 and membrane 240 are
supported by structural layer 236, which is formed of an insulating
material. Structural layer 236 is formed of tetraethyl
orthosilicate (TEOS) oxide in one embodiment. In other embodiments,
structural layer 236 may be formed of oxides or nitrides. In
alternative embodiments, structural layer 236 is formed of a
polymer. Isolation 234 is formed between substrate 232 and
structural layer 236. Isolation 234 is a nitride, such as silicon
nitride, in some embodiments. In other embodiments, isolation 234
is any type of insulating etch resistant material. For example,
substrate 232 may undergo a backside etch through the whole
substrate where isolation 234 is used as an etch stop. In such
embodiments, isolation 234 is a material that is selectively etched
much slower than the material of substrate 232.
[0080] According to various embodiments, substrate 232 is silicon.
Substrate 232 may also be any type of semiconductor. In further
embodiments, substrate 232 may be a polymer substrate or a laminate
substrate.
[0081] In various embodiments, backplate 238 is formed of
conductive layer 242 and includes perforations 241. Backplate 238
may be a rigid backplate structure that remains substantially
un-deflected while membrane 240 deflects in relation to acoustic
signals. In various embodiments, backplate 238 has a greater
thickness than membrane 240. Conductive layer 242 is polysilicon in
some embodiments. In other embodiments, conductive layer 242 is any
type of semiconductor, such as doped semiconductor layer. In still
further embodiments, conductive layer 242 is formed of a metal,
such as aluminum, silver, gold, or platinum, for example.
[0082] According to various embodiments, metallization 254 is
formed in a via in structural layer 236 and forms an electrical
contact with conductive layer 248. Similarly, metallization 256 is
formed in a via in structural layer 236 and forms an electrical
contact with conductive layer 244, metallization 258 is formed in a
via in structural layer 236 and forms an electrical contact with
conductive layer 242, and metallization is formed in a via in
structural layer 236 and forms an electrical contact with substrate
232. Metallization 254, metallization 256, metallization 258, and
metallization 260 are formed of aluminum in some embodiments. In
other embodiments, metallization 254, metallization 256,
metallization 258, and metallization 260 are formed of any type of
metal suitable for the fabrication process and other materials used
in MEMS acoustic transducer 231a.
[0083] In various embodiments, dipole electrodes 250 operate with
backplate 238 as described hereinabove in reference to FIGS. 2a,
3a, 3b, and 4b for example. In additional embodiments, backplate
238 and membrane 240 may flipped such that backplate 238 is above
and membrane 240 is below and closer to cavity 233. In various
embodiments, a sound port may be included below cavity 233. In
other embodiments, a sound port may be included above MEMS acoustic
transducer 231a.
[0084] Membrane 240 is depicted at a cross-section showing
electrical connections 252, as similarly described hereinabove in
reference to FIG. 6b, however, sections of membrane 240 also
include patterned electrodes as described hereinabove in reference
to FIGS. 4b and 6a, for example.
[0085] In various embodiments, MEMS acoustic transducer 231a is a
MEMS microphone. In other embodiments, MEMS acoustic transducer
231a is a MEMS microspeaker. In such embodiments, the size of the
membrane and the separation distance between backplate 238 and
membrane 240 may be larger for the MEMS microspeaker than for the
MEMS microphone.
[0086] FIG. 7b illustrates MEMS acoustic transducer 231b including
a single backplate 238 and membrane 240. According to various
embodiments, MEMS acoustic transducer 231b includes substrate 232,
isolation 234, structural layer 236, backplate 238, membrane 240,
metallization 253, metallization 255, metallization 257,
metallization 259, and metallization 260. MEMS acoustic transducer
231b is similar to MEMS acoustic transducer 231a, with the
exception that backplate 238 is a multilayer semiconductor
structure that includes dipole electrodes 250 and membrane 240 does
not include dipole electrodes.
[0087] In various embodiments, membrane 240 is formed of conductive
layer 262. Conductive layer 262 is polysilicon in some embodiments.
In other embodiments, conductive layer 262 is any type of
semiconductor, such as doped semiconductor layer. In still further
embodiments, conductive layer 262 is formed of a metal, such as
aluminum, silver, gold, or platinum, for example.
[0088] According to various embodiments, backplate 238 includes a
five layer semiconductor stack including conductive layer 264,
insulating layer 266, conductive layer 268, insulating layer 270,
and conductive layer 272. Backplate 238 includes perforations 241.
In various embodiments, dipole electrodes 250 are formed from
conductive layer 264 and interconnected with electrical connections
252, which are also formed from conductive layer 264.
[0089] In various embodiments, conductive layer 268 is polysilicon
in some embodiments. In other embodiments, conductive layer 268 is
any type of semiconductor, such as doped semiconductor layer. In
still further embodiments, conductive layer 268 is formed of a
metal, such as aluminum, silver, gold, or platinum, for example. In
various embodiments, conductive layer 268, insulating layer 266,
and insulating layer 270 are combined into a single insulating
layer with a similar combination of layers as membrane 240, for
example.
[0090] In various embodiments, insulating layer 266 and insulating
layer 270 are formed on the top surface and bottom surface of
conductive layer 268, respectively. Insulating layer 266 and
insulating layer 270 are formed of silicon nitride or silicon
dioxide. In further embodiments, insulating layer 266 and
insulating layer 270 may be formed of any type of oxide or nitride.
Insulating layer 266 and insulating layer 270 may be any type of
insulator suitable for fabrication and operation with embodiment
multi-electrode transducers, such as a polymer in alternative
embodiments.
[0091] Conductive layer 264 and conductive layer 272 may be formed
as conductive layers on the top and bottom surfaces of insulating
layer 266 and insulating layer 270, respectively. Further,
conductive layer 264 and conductive layer 272 are patterned to form
dipole electrodes 250 and electrical connections 252. Conductive
layer 264 and conductive layer 272 are formed of polysilicon in one
embodiment. Conductive layer 264 and conductive layer 272 are
formed of metal in other embodiments. In such embodiments,
conductive layer 264 and conductive layer 272 are formed of
aluminum, silver, or gold. In other embodiments, conductive layer
264 and conductive layer 272 are formed of any conductor suitable
for fabrication and operation with embodiment multi-electrode
transducers, such as other metals or doped semiconductors.
[0092] Backplate 238 is depicted at a cross-section showing
electrical connections 252, as similarly described hereinabove in
reference to FIG. 6d, however, sections of backplate 238 also
include patterned electrodes as described hereinabove in reference
to FIGS. 4b and 6c, for example.
[0093] Metallization 253, metallization 255, metallization 257, and
metallization 259 may be formed as described hereinabove in
reference to metallization 254, metallization 256, metallization
258, and metallization 260 in FIG. 6a. Metallization 253 is formed
in a via in structural layer 236 and forms an electrical contact
with conductive layer 262, metallization 255 is formed in a via in
structural layer 236 and forms an electrical contact with
conductive layer 264, metallization 257 is formed in a via in
structural layer 236 and forms an electrical contact with
conductive layer 268, and metallization 259 is formed in a via in
structural layer 236 and forms an electrical contact with 272.
[0094] FIG. 7c illustrates MEMS acoustic transducer 231c including
a single backplate 238 and membrane 240. According to various
embodiments, MEMS acoustic transducer 231c includes substrate 232,
isolation 234, structural layer 236, backplate 238, membrane 240,
metallization 254, metallization 258, metallization 260, and
metallization 278. MEMS acoustic transducer 231C is similar to MEMS
acoustic transducer 231a, with the exception that membrane 240
includes both poles of dipole electrodes 250 formed on a same
surface. In such embodiments, dipole electrodes 250 may be formed
fully on the top surface or fully on the bottom surface of
insulating layer 246.
[0095] In various embodiments, membrane 240 includes insulating
layer 246, conductive layer 248, insulating layer 274, and
conductive layer 276. Insulating layer 246 and conductive layer 248
are formed as described hereinabove in reference to FIG. 7c.
Insulating layer 274 is formed on a top surface of conductive layer
248. Further, conductive layer 276 is formed on a top surface of
insulating layer 274. Insulating layer 274 is formed of silicon
nitride or silicon dioxide. In further embodiments, insulating
layer 274 may be formed of any type of oxide or nitride. Insulating
layer 274 may be any type of insulator suitable for fabrication and
operation with embodiment multi-electrode transducers, such as a
polymer in alternative embodiments.
[0096] Conductive layer 248 and conductive layer 276 are patterned
to form dipole electrodes 250 and electrical connections 252.
Conductive layer 276 is formed of polysilicon in one embodiment.
Conductive layer 276 is formed of metal in other embodiments. In
such embodiments, conductive layer 276 is formed of aluminum,
silver, or gold. In other embodiments, conductive layer 276 is
formed of any conductor suitable for fabrication and operation with
embodiment multi-electrode transducers, such as other metals or
doped semiconductors.
[0097] Metallization 278 may be formed as described hereinabove in
reference to metallization 254, metallization 256, metallization
258, and metallization 260 in FIG. 6a. Metallization 278 is formed
in a via in structural layer 236 and forms an electrical contact
with conductive layer 276.
[0098] Membrane 240 is depicted at a cross-section showing
electrical connections 252, as similarly described hereinabove in
reference to FIG. 6j, however, sections of membrane 240 also
include patterned electrodes as described hereinabove in reference
to FIGS. 4b and 6i, for example.
[0099] FIG. 7d illustrates MEMS acoustic transducer 231d including
two backplates, backplate 238 and backplate 239, and membrane 240.
According to various embodiments, MEMS acoustic transducer 231d
includes substrate 232, isolation 234, structural layer 236,
backplate 238, backplate 239, and membrane 240. MEMS acoustic
transducer 231d is similar to MEMS acoustic transducer 231b, with
the addition of second backplate 239.
[0100] In order to improve clarity, FIG. 7d illustrates MEMS
acoustic transducer 231d at a cross-section that does not show
electrical connections 252 or metallization for forming electrical
contacts with conductive layer 248, conductive layer 268, or
conductive layer 244 of backplate 238; conductive layer 262 of
membrane 240; or conductive layer 248, conductive layer 268, or
conductive layer 244 of backplate 239. However, such electrical
connections 252 and metallization is included in various
embodiments. For example, FIG. 7d illustrates MEMS acoustic
transducer 231d with backplates 238 and 239 having semiconductor
stacks as similarly described hereinabove in reference to FIG. 6c,
however, sections of backplates 238 and 239 also include patterned
electrodes as described hereinabove in reference to FIGS. 4b and
6d.
[0101] Backplate 238 and backplate 239 are illustrated with
identical numerals for identification of the various structures and
layers. Thus, the description provided hereinabove of the various
structures and layers in reference to backplate 238 also applies to
the commonly numbered layers and structures of backplate 239.
However, one of ordinary skill in the art will recognize that the
various layers, for example, of backplate 238 and backplate 239 are
not the same layer and may be formed and patterned separately in
various embodiments.
[0102] FIG. 7e illustrates MEMS acoustic transducer 231e including
backplate 239 and membrane 240. According to various embodiments,
MEMS acoustic transducer 231e includes substrate 232, isolation
234, structural layer 236, backplate 238, and membrane 240. MEMS
acoustic transducer 231e is similar to MEMS acoustic transducer
231a, with patterned electrodes on both backplate 239 and membrane
240.
[0103] In order to improve clarity, FIG. 7e illustrates MEMS
acoustic transducer 231e at a cross-section that does not show
electrical connections 252 or metallization for forming electrical
contacts with conductive layer 248, conductive layer 244,
conductive layer 264; or conductive layer 272. However, such
electrical connections 252 and metallization is included in various
embodiments. For example, FIG. 7e illustrates MEMS acoustic
transducer 231e with membrane 240 and backplate 238 having
semiconductor stacks as similarly described hereinabove in
reference to FIG. 6a, however, sections of membrane 240 and
backplates 238 also include patterned electrodes as described
hereinabove in reference to FIGS. 4b and 6b.
[0104] Membrane 240 is illustrated with identical numerals for
identification of the various structures and layers. Thus, the
description provided hereinabove of the various structures and
layers in reference to membrane 240 also applies to the commonly
numbered layers and structures. Similarly, backplate 238 is
illustrated with identical numerals for identification of the
various structures and layers, where insulating layer 280 replaces
insulating layer 266, conductive layer 268, and insulating layer
270. In various embodiments, insulating layer 280 may include any
of the features of insulating layer 246 or insulating layer 266 and
insulating layer 270, as described hereinabove. In particular
embodiments, insulating layer 280 is thicker than insulating layer
246. For the other elements of backplate 238, the description
provided hereinabove of the various structures and layers in
reference to backplate 238 also applies to the commonly numbered
layers and structures.
[0105] The embodiments described in reference to FIGS. 7a, 7b, 7c,
7d, and 7e may be modified to include any of the embodiment
electrode structures described hereinabove in reference to FIGS.
3a-3f, 4a-4d, 5, and 6a-6l. In various such embodiments, both the
membrane and the backplate, or backplates in the case of a
dual-backplate structure, may include any of the embodiment
electrode structures described hereinabove in reference to FIGS.
3a-3f, 4a-4d, 5, and 6a-6l.
[0106] FIG. 8 illustrates a block diagram of an embodiment method
of forming a MEMS transducer using fabrication sequence 300 that
includes steps 302-322. According to various embodiments,
fabrication sequence 300 begins with a substrate in step 302. The
substrate may be formed of a semiconductor, such as silicon, or as
another material, such as a polymer for example. An etch stop layer
is formed on the substrate in step 304. The etch stop layer may be
silicon nitride or silicon oxide, for example. In step 306, a first
backplate is formed by forming and patterning layers for the first
backplate. In various embodiments, the first backplate may be
formed and patterned according to any of the embodiments described
hereinabove in reference to FIGS. 6a-6l, for example. Further
description of embodiment processing steps for forming the first
backplate are described herein below in reference to FIGS. 9a, 9b,
and 9c.
[0107] In various embodiments, step 308 includes forming and
patterning a structural material, such as TEOS oxide. Forming and
patterning in step 308 is performed in order to provide spacing for
a membrane. The structural layer may be patterned in order to form
anti-stiction bumps for the membrane. In addition, the structural
layer formed in step 308 may include multiple depositions and a
planarization step, such as a chemical mechanical polish (CMP).
Step 310 includes forming the membrane layer and patterning the
membrane. The membrane layer may be formed of polysilicon, for
example. In other embodiments, the membrane layer may be formed of
other conductive materials, such as a doped semiconductor or a
metal, for example. In various embodiments, the membrane may be
formed and patterned according to any of the embodiments described
hereinabove in reference to FIGS. 6a-6l, for example. Further
description of embodiment processing steps for forming the membrane
are described herein below in reference to FIGS. 9a, 9b, and 9c.
Patterning the membrane layer in step 310 may include a
photolithographic process, for example, that defines the membrane
shape or structure. The membrane may include anti-stiction bumps
based on the structure formed in step 308.
[0108] In various embodiments, step 312 includes forming and
patterning additional structural material, such as TEOS oxide.
Similar to step 308, the structural material may be formed and
patterned in step 312 to space a second backplate from the membrane
and provide anti-stiction bumps in the second backplate. Step 314
includes forming and patterning the layers of the second backplate.
In some embodiments, forming and patterning in step 314 includes
deposition of layers and photolithographic patterning, for example.
In various embodiments, the second backplate may be omitted. In
other embodiments where the second backplate is not omitted, the
second backplate may be formed and patterned according to any of
the embodiments described hereinabove in reference to FIGS. 6a-6l,
for example. Further description of embodiment processing steps for
forming the second backplate are described herein below in
reference to FIGS. 9a, 9b, and 9c.
[0109] Following step 314, step 316 includes forming and patterning
additional structural material in various embodiments. The
structural material may be TEOS oxide. In some embodiments, the
structural material is deposited as a sacrificial material or a
masking material for subsequent etch or patterning steps. Step 318
includes forming and patterning contact pads. Forming and
patterning the contact pads in step 318 may include etching contact
holes in the existing layers to provide openings to the second
backplate, membrane, first backplate, and substrate, as well as
openings to the conductive layers formed as part of the first
backplate, membrane, or second backplate to implement various
electrodes or dipole electrodes as described hereinabove in
reference to the other figures. After forming the openings to each
respective structure or layer, the contact pads may be formed by
depositing a conductive material, such as a metal, in the openings
and patterning the conductive material to form separate contact
pads. The metal may be aluminum, silver, or gold in various
embodiments. Alternatively, the metallization may include a
conductive paste, for example, or other metals, such as copper.
[0110] In various embodiments, step 320 includes performing a
backside etch, such as a Bosch etch. The backside etch forms a
cavity in the substrate that may be coupled to a sound port for the
fabricated microphone or may form a reference cavity. Step 322
includes performing a release etch to remove the structural
materials protecting and securing the first backplate, membrane,
and second backplate. Following the release etch in step 322, the
membrane may be free to move in some embodiments.
[0111] As described hereinabove, fabrication sequence 300 may be
modified in specific embodiments to include only a single backplate
and membrane. Those of skill in the art will readily appreciate
that numerous modifications may be made to the general fabrication
sequence described hereinabove in order to provide various benefits
and modifications known to those of skill in the art while still
including various embodiments of the present invention. In some
embodiments, fabrication sequence 300 may be implemented to form a
MEMS microspeaker or a MEMS microphone, for example, or a pressure
sensor in other embodiments. In still other embodiments,
fabrication sequence 300 may be implemented to form any type of
MEMS transducer including embodiment electrode structures as
described herein.
[0112] FIGS. 9a, 9b, and 9c illustrate block diagrams of embodiment
methods of forming multi-electrode elements using fabrication
sequence 330, fabrication sequence 350, and fabrication sequence
370. According to various embodiments, fabrication sequence 330,
fabrication sequence 350, and fabrication sequence 370 form
multi-electrode elements as descried hereinabove in reference to
FIGS. 6a-6l. Further, fabrication sequence 330, fabrication
sequence 350, and fabrication sequence 370 described embodiment
fabrication sequences for forming the first backplate in step 306,
forming the membrane in step 310, or forming the second backplate
in step 314, as described hereinabove in reference to FIG. 8.
[0113] FIG. 9a illustrates fabrication sequence 330 for forming a
three layer structure with patterned electrodes, such as a
backplate or membrane in some embodiments. For example, fabrication
sequence 330 may be used to form multi-electrode element 200a or
multi-electrode element 200e as described hereinabove in reference
to FIGS. 6a, 6b, and 6h. Fabrication sequence 330 includes steps
332-342. According to various embodiments, step 332 includes
depositing or forming a first layer on a first surface. The first
layer is a conductive layer. In such embodiments, a patternable
structural material, such as TEOS oxide, may be the first surface
as described hereinabove in reference to steps 308, 312, or 316 in
FIG. 8, and the first layer is formed or deposited on the TEOS
oxide layer. The first layer is polysilicon in some embodiments. In
other embodiments, the first layer is a metal such as silver, gold,
aluminum, or platinum. In further embodiments, the first layer is
any type of semiconductor, such as a doped semiconductor material.
In alternative embodiments, the first layer may be another metal,
such as copper. The first layer may be deposited or formed using
any of the methods known to those of skill in the art to be
compatible with the material selected for deposition or formation,
such as electroplating, chemical vapor deposition (CVD), or
physical vapor deposition (PVD), for example.
[0114] Following step 332, step 334 includes patterning the first
layer to form patterned electrodes. In such embodiments, the
patterning of step 334 may include a lithographic process including
applying a photoresist, patterning the photoresist using a mask for
exposure and a developer solution, and etching the first layer
according to the patterned photoresist. In various embodiments,
step 334 may include photolithography, electron beam lithography,
ion beam or lithography. In still further embodiments, step 334 may
include x-ray lithography, mechanical imprint patterning, or
microscale (or nanoscale) printing techniques. Still further
approaches for patterning the first layer may be used in some
embodiments, as will be readily appreciated by those of skill in
the art. In step 334, the first layer may be patterned to form
concentric circles, as described hereinabove in reference to FIGS.
4a, 4b, 4c, 4d, and 5.
[0115] In some embodiments, the first layer may also include
electrical connections as described hereinabove in reference to
first electrical connections 208 in FIGS. 6b. Thus, step 334 may
include patterning the electrical connections. In various
embodiments, the electrical connections may include a thinned first
layer, as described hereinabove in reference to second electrical
connections 210 in FIG. 6g, or an additional forming and patterning
step with another material.
[0116] Before step 336, an additional step of depositing or forming
a sacrificial layer and performing a planarization step on the
sacrificial layer and the first layer may be included. For example,
a chemical mechanical polish (CMP) may be applied to the
sacrificial layer and the first layer. In various embodiments, step
336 includes depositing or forming a second layer on the patterned
first layer. The second layer is an insulating layer.
[0117] In some embodiments, the second layer is a nitride, such as
silicon nitride. In other embodiments, the second layer is an
oxide, such as silicon oxide. The second layer may be another type
of suitable dielectric or insulator in further embodiments. In an
alternative embodiment, the second layer may be formed of a
polymer. In one embodiment, the second layer may be a TEOS oxide.
In various embodiments, the second layer may be deposited or formed
using any of the methods known to those of skill in the art to be
compatible with the material selected for deposition or formation,
such as CVD, PVD, or thermal oxidation for example.
[0118] Step 338 includes patterning the second layer. Patterning
the second layer may be performed using any of the techniques
described in reference to step 334. The second layer may be
patterned to form a membrane or a backplate in some embodiments.
For example, the second layer may be patterned to form a circular
membrane. In embodiments where fabrication sequence 330 is used to
form a backplate for a MEMS acoustic transducer, the second layer
may also be patterned to form perforations. Similarly, in other
embodiments involving other structures for other types of
transducers, the second layer may be patterned according to the
specific type of transducer.
[0119] Following step 338, step 340 includes depositing or forming
a third layer on top of the second layer. The third layer is a
conductive layer that may be formed using any of the techniques or
materials described in reference to step 332.
[0120] Step 342 includes patterning the third layer to form
patterned electrodes and electrical connections. Patterning the
third layer may be performed using any of the techniques described
in reference to step 334. In step 342, the third layer may be
patterned to form concentric circles, or other patterns, as
described hereinabove in reference to FIGS. 4a, 4b, 4c, 4d, and 5.
In various embodiments the patterned electrodes formed in steps 334
and 342 may together form positive and negative poles for dipole
electrodes, such as described hereinabove in reference to FIGS. 3a
and 6a, for example.
[0121] In various embodiments, fabrication sequence 330 may be used
to form a backplate or a membrane. In some embodiments, either the
first layer or the third layer may be omitted. For examples, in
embodiments for forming multi-electrode plates or structures as
described hereinabove in reference to FIGS. 3c, 3d, 4a, 4c, 4d, and
5, the first layer or the second layer may be omitted. Fabrication
sequence 330 may also be used to form a layered multi-electrode
structure for other types of MEMS transducers.
[0122] FIG. 9b illustrates fabrication sequence 350 for forming a
five layer structure with patterned electrodes, such as a backplate
or membrane in some embodiments. For example, fabrication sequence
350 may be used to form multi-electrode element 200b as described
hereinabove in reference to FIGS. 6c and 6d. Fabrication sequence
350 includes steps 352-369. According to various embodiments, step
352 includes depositing or forming a first layer on a first
surface. In such embodiments, a patternable structural material,
such as TEOS oxide, may be the first surface as described
hereinabove in reference to steps 308, 312, or 316 in FIG. 8, and
the first layer is formed or deposited on the TEOS oxide layer. The
first layer is a conductive layer that may be formed using any of
the techniques or materials described hereinabove in reference to
step 332 in FIG. 9a.
[0123] Following step 352, step 354 includes patterning the first
layer to form patterned electrodes and electrical connections.
Patterning the first layer in step 354 may be performed using any
of the techniques described hereinabove in reference to step 334 in
FIG. 9a. In step 354, the first layer may be patterned to form
concentric circles, as described hereinabove in reference to FIGS.
4a, 4b, 4c, 4d, and 5.
[0124] Before step 356, an additional step of depositing or forming
a sacrificial layer and performing a planarization step on the
sacrificial layer and the first layer may be included. For example,
a chemical mechanical polish (CMP) may be applied to the
sacrificial layer and the first layer. In various embodiments, step
356 includes depositing or forming a second layer on the patterned
first layer. The second layer in step 356 is an insulating layer
that may be formed using any of the techniques or materials
described hereinabove in reference to step 336 in FIG. 9a. Step 358
includes patterning the second layer. Patterning the second layer
in step 358 may be performed using any of the techniques described
hereinabove in reference to step 334 in FIG. 9a.
[0125] Following step 358, step 360 includes depositing or forming
a third layer on top of the second layer. The third layer in step
360 is a conductive layer that may be formed using any of the
techniques or materials described hereinabove in reference to step
332 in FIG. 9a. In particular embodiments, the third layer is a
polysilicon layer that is formed using a CVD process. In such
particular embodiments, the polysilicon third layer is thicker than
the second layer and a fourth layer. For example, the third layer
is the structural layer for a membrane or a backplate, while the
second and fourth layers are thin insulation layers. Step 362
includes patterning the third layer. Patterning the third layer in
step 362 may be performed using any of the techniques described
hereinabove in reference to step 334 in FIG. 9a.
[0126] In various embodiments, step 364 includes depositing or
forming a fourth layer on top of the third layer. The fourth layer
in step 364 is an insulating layer that may be formed using any of
the techniques or materials described hereinabove in reference to
step 336 in FIG. 9a. Step 366 includes patterning the fourth layer.
Patterning the fourth layer in step 366 may be performed using any
of the techniques described hereinabove in reference to step 334 in
FIG. 9a.
[0127] According to various embodiments, the second layer, the
third layer, and the fourth layer may together form a backplate or
a membrane for a MEMS acoustic transducer. Thus, the second layer,
the third layer, and the fourth layer may be patterned to form a
membrane or a backplate in such embodiments. For example, the
second layer, the third layer, and the fourth layer may be
patterned, in each separate patterning step or together in a single
patterning step, to form a circular membrane. In embodiments where
fabrication sequence 350 is used to form a backplate for a MEMS
acoustic transducer, the second layer, the third layer, and the
fourth layer may also be patterned to form perforations. Similarly,
in other embodiments involving other structures for other types of
transducers, the second layer, the third layer, and the fourth
layer may be patterned according to the specific type of
transducer.
[0128] Step 368 includes depositing or forming a fifth layer on top
of the fourth layer. The fifth layer is a conductive layer that may
be formed using any of the techniques or materials described
hereinabove in reference to step 332 in FIG. 9a. Following step
368, step 369 includes patterning the fifth layer to form patterned
electrodes and electrical connections. Patterning the fifth layer
in step 369 may be performed using any of the techniques described
hereinabove in reference to step 334 in FIG. 9a. In step 369, the
fifth layer may be patterned to form concentric circles, as
described hereinabove in reference to FIGS. 4a, 4b, 4c, 4d, and 5.
In various embodiments the patterned electrodes formed in steps 354
and 369 may together form positive and negative poles for dipole
electrodes, such as described hereinabove in reference to FIGS. 3a
and 6c, for example.
[0129] In various embodiments, fabrication sequence 350 may be used
to form a backplate or a membrane. In some embodiments, either the
first and second layers or the fourth and fifth layers may be
omitted. For examples, in embodiments for forming multi-electrode
plates or structures as described hereinabove in reference to FIGS.
3c, 3d, 4a, 4c, 4d, and 5, the first and second layers or the
fourth and fifth layers may be omitted. Fabrication sequence 350
may also be used to form a layered multi-electrode structure for
other types of MEMS transducers.
[0130] FIG. 9c illustrates fabrication sequence 370 for forming a
six layer structure with patterned electrodes, such as a backplate
or membrane in some embodiments. For example, fabrication sequence
370 may be used to form multi-electrode element 200c or
multi-electrode elements 200d as described hereinabove in reference
to FIGS. 6e, 6f, 6g, 6k, and 6l. Fabrication sequence 370 includes
steps 372-394. According to various embodiments, step 372 includes
depositing or forming a first layer on a first surface. In such
embodiments, a patternable structural material, such as TEOS oxide,
may be the first surface as described hereinabove in reference to
steps 308, 312, or 316 in FIG. 8, and the first layer is formed or
deposited on the TEOS oxide layer. The first layer in step 372 is
an insulating layer that may be formed using any of the techniques
or materials described hereinabove in reference to step 336 in FIG.
9a. Step 374 includes patterning the first layer. Patterning the
first layer in step 374 may be performed using any of the
techniques described hereinabove in reference to step 334 in FIG.
9a.
[0131] Following step 374, step 376 includes depositing or forming
a second layer on top of the first layer. The second layer in step
376 is a conductive layer that may be formed using any of the
techniques or materials described hereinabove in reference to step
332 in FIG. 9a and in reference to step 360 in FIG. 9b. In
particular embodiments, the second layer is a polysilicon layer
that is formed using a CVD process. In such particular embodiments,
the polysilicon second layer is thicker than the first layer and a
third layer. For example, the second layer is the structural layer
for a membrane or a backplate, while the first and third layers are
thin insulation layers. Step 378 includes patterning the second
layer. Patterning the second layer in step 378 may be performed
using any of the techniques described hereinabove in reference to
step 334 in FIG. 9a.
[0132] In various embodiments, step 380 includes depositing or
forming a third layer on top of the second layer. The third layer
in step 380 is an insulating layer that may be formed using any of
the techniques or materials described hereinabove in reference to
step 336 in FIG. 9a. Step 382 includes patterning the third layer.
Patterning the third layer in step 382 may be performed using any
of the techniques described hereinabove in reference to step 334 in
FIG. 9a.
[0133] According to various embodiments, the first layer, the
second layer, and the third layer may together form a backplate or
a membrane for a MEMS acoustic transducer. Thus, the first layer,
the second layer, and the third layer may be patterned to form a
membrane or a backplate in such embodiments. For example, the first
layer, the second layer, and the third layer may be patterned, in
each separate patterning step or together in a single patterning
step, to form a circular membrane. In embodiments where fabrication
sequence 370 is used to form a backplate for a MEMS acoustic
transducer, the first layer, the second layer, and the third layer
may also be patterned to form perforations. Similarly, in other
embodiments involving other structures for other types of
transducers, the first layer, the second layer, and the third layer
may be patterned according to the specific type of transducer.
[0134] In various embodiments, step 384 includes depositing or
forming a fourth layer on top of the third layer. The fourth layer
is a conductive layer that may be formed using any of the
techniques or materials described hereinabove in reference to step
332 in FIG. 9a. Following step 384, step 386 includes patterning
the fourth layer to form patterned electrodes and electrical
connections. Patterning the fourth layer in step 386 may be
performed using any of the techniques described hereinabove in
reference to step 334 in FIG. 9a. In step 386, the fourth layer may
be patterned to form concentric circles, or other shapes, as
described hereinabove in reference to FIGS. 4a, 4b, 4c, 4d, and
5.
[0135] In some embodiments, the fourth layer may also include
electrical connections as described hereinabove in reference to
second electrical connections 210 in FIGS. 6f and 6g. Thus, step
386 may include patterning the electrical connections. In various
embodiments, the electrical connections may include a thinned
fourth layer, as described hereinabove in reference to second
electrical connections 210 in FIG. 6g, or an additional forming and
patterning step with another material.
[0136] Before step 388, an additional step of depositing or forming
a sacrificial layer and performing a planarization step on the
sacrificial layer and the fourth layer may be included. For
example, a CMP may be applied to the sacrificial layer and the
fourth layer. In various embodiments, step 388 includes depositing
or forming a fifth layer on the patterned fourth layer. The fifth
layer in step 388 is an insulating layer that may be formed using
any of the techniques or materials described hereinabove in
reference to step 336 in FIG. 9a. Step 390 includes patterning the
fifth layer to form insulation on the patterned electrodes of step
386. Patterning the fifth layer in step 390 may be performed using
any of the techniques described hereinabove in reference to step
334 in FIG. 9a. In step 390, the fifth layer may be patterned to
form concentric circles matching and on top of the concentric
circles of the patterned electrodes of step 386, as described
hereinabove in reference to FIGS. 4a, 4b, 4c, 4d, and 5.
[0137] Before step 392, as before step 388, an additional step of
depositing or forming a sacrificial layer and performing a
planarization step on the sacrificial layer and the fifth layer may
be included. For example, a CMP may be applied to the sacrificial
layer and the fifth layer. Step 392 includes depositing or forming
a sixth layer on top of the fifth layer. The sixth layer is a
conductive layer that may be formed using any of the techniques or
materials described hereinabove in reference to step 332 in FIG.
9a.
[0138] Following step 392, step 394 includes patterning the sixth
layer to form patterned electrodes on top of the patterned
electrodes of step 386 and the insulation of step 390. Step 394 may
also include forming patterned electrical connections. Patterning
the sixth layer in step 394 may be performed using any of the
techniques described hereinabove in reference to step 334 in FIG.
9a. In step 394, the sixth layer may be patterned to form
concentric circles on top of the concentric circles of the
patterned electrode in step 386, as described hereinabove in
reference to FIG. 4b. In various embodiments the patterned
electrodes formed in steps 386 and 394 may together form positive
and negative poles for dipole electrodes, such as described
hereinabove in reference to FIGS. 3b and 6e, for example.
[0139] In some embodiments, the sixth layer may also include
electrical connections as described hereinabove in reference to
third electrical connections 224 in FIGS. 6f and 6g. Thus, step 394
may include patterning the electrical connections. In various
embodiments, the electrical connections may include a thinned sixth
layer, as described hereinabove in reference to third electrical
connections 224 in FIG. 6g, or an additional forming and patterning
step with another material.
[0140] In other embodiments, the patterned electrodes formed in
step 394 may not be placed on top of the patterned electrodes of
step 386. Instead, step 394 includes patterning the electrodes in,
for example, concentric circles offset from the concentric circles
of the patterned electrodes of step 386. For example, step 386 and
step 394 may together include patterning electrodes as described
hereinabove in reference to FIGS. 4a, 6k, and 6l.
[0141] In various embodiments, fabrication sequence 370 may be used
to form a backplate or a membrane. In some embodiments, the first
layer may be omitted. For examples, in embodiments for forming
multi-electrode plates or structures as described hereinabove in
reference to FIGS. 3b, 3f, 6e, 6f, and 6g, the first layer that is
an insulating layer connected to the bottom side of the plate
(membrane or backplate) may be omitted. Fabrication sequence 370
may also be used to form a layered multi-electrode structure for
other types of MEMS transducers.
[0142] In particular embodiments, fabrication sequence 370 includes
forming patterned dipole electrodes on a top surface, i.e., as
layers four, five, and six, as described hereinabove in reference
to FIGS. 6e, 6f, and 6g, for example. In other embodiments,
fabrication sequences 370 may be modified to form the patterned
dipole electrodes on a bottom surface. In such embodiments, steps
384-394 may be performed first and steps 372-382 may be performed
second. Thus, the first layer, the second layer, and the third
layer may form a membrane or a backplate, for example, and dipole
electrodes may be formed on either the top surface or the bottom
surface of the membrane or the backplate formed by the first layer,
the second layer, and the third layer.
[0143] In further particular embodiments, fabrication sequence 370
may be modified to form structures as described hereinabove in
reference to FIGS. 6i and 6j. In such embodiments, the first layer
and the second layer, formed in steps 372-378, may be omitted.
Thus, the third layer may be formed first. In such embodiments, the
third layer is formed as a thicker structural layer as described
and shown hereinabove in reference to insulating layer 202 in FIGS.
6i and 6j.
[0144] In other embodiments, structure variations and material
alternatives are envisioned for fabrication sequence 330,
fabrication sequence 350, and fabrication sequence 370. In some
alternative embodiments, a backplate or membrane may be formed of
any number of layers, conductive or insulating. For example, in
some embodiments, the backplate or membrane may include layers of
metals, semiconductors, or dielectrics. A dielectric layer may be
used to separate a conductive sensing layer from electrodes. In
some embodiments, the backplate or membrane may be formed of
silicon on insulator (SOI) or metal and dielectric layers.
FIGS. 10a and 10b illustrate force plots 400 and 410 of two
transducers. FIG. 10a illustrates force plot 400 of a typical
transducer without a dipole electrode including electrostatic force
curve 402, membrane spring force curve 404, and summation force
curve 406, which is the sum of electrostatic force curve 402 and
membrane spring force curve 404. As shown, summation force curve
406 becomes very negative, i.e., attractive, for smaller distances
between the membrane and backplate. This behavior leads to pull-in
or collapse of the backplate and membrane and is caused by the
relationship between the electrostatic force and the distance
between the charged plates, which includes the distance in the
denominator of the electrostatic force equation.
[0145] FIG. 10b illustrates force plot 410 of an embodiment
multi-electrode transducer with a dipole electrode including
electrostatic force curve 412, membrane spring force curve 414, and
summation force curve 416, which is the sum of electrostatic force
curve 412 and membrane spring force curve 414. As shown, summation
force curve 416 becomes increasingly positive, i.e., repulsive, for
smaller distances between the membrane and backplate. This behavior
of various embodiments prevents pull-in or collapse of the
backplate and membrane and is caused by the presence of various
embodiment dipole electrodes described hereinabove in reference to
the other figures.
[0146] According to an embodiment, a MEMS transducer includes a
stator, a rotor spaced apart from the stator, and a multi-electrode
structure including electrodes with different polarities. The
multi-electrode structure is formed on one of the rotor and the
stator and is configured to generate a repulsive electrostatic
force between the stator and the rotor. Other embodiments include
corresponding systems and apparatus, each configured to perform
corresponding embodiment methods.
[0147] Implementations may include one or more of the following
features. In various embodiments, the stator includes a backplate,
the rotor includes a membrane, and the MEMS transducer is a MEMS
microphone or a MEMS microspeaker. In some embodiments, the
multi-electrode structure includes a first plurality of dipole
electrodes. In other embodiments, the rotor includes the first
plurality of dipole electrodes and the stator includes a conductive
layer. In further embodiments, the stator includes the first
plurality of dipole electrodes and the rotor includes a conductive
layer. In specific embodiments, the stator includes the first
plurality of dipole electrodes and the rotor includes a second
plurality of dipole electrodes.
[0148] In various embodiments, each dipole electrode of the first
plurality of dipole electrodes includes a positive pole and a
negative pole formed on a same surface of the rotor or the stator.
In some embodiments, for each dipole electrode of the first
plurality of dipole electrodes, the positive pole and the negative
pole are separated by an insulating layer and formed as a layered
stack on the same surface of the rotor or the stator. In further
embodiments, for each dipole electrode of the first plurality of
dipole electrodes, the positive pole and the negative pole are
formed spaced apart on the same surface of the rotor or the
stator.
[0149] In various embodiments, the first plurality of dipole
electrodes is formed as concentric electrodes with alternative
positive and negative poles. In some embodiments, each dipole
electrode of the first plurality of dipole electrodes includes a
positive pole formed on a first surface and a negative pole formed
on a second surface, where the first surface is an opposite surface
of the second surface and both the first surface and the second
surface are on either the rotor or the stator. In further
embodiments, the MEMS transducer further includes an insulating
layer formed between the first surface and the second surface. In
still further embodiments, the MEMS transducer further includes a
conductive layer formed with insulating layers formed between the
first surface and the conductive layer and between the second
surface and the conductive layer. In such embodiments, the first
plurality of dipole electrodes may be formed as concentric
electrodes on the first surface and on the second surface. The
multi-electrode structure may include a first discontinuous
electrode formed of a conductive layer on a first surface of the
rotor or the stator, where the first discontinuous electrode
includes a plurality of first concentric electrode portions coupled
to a first electrode connection and including a break in each
electrode portion of the plurality of first concentric electrode
portions.
[0150] In particular embodiments, the multi-electrode structure
further includes a second discontinuous electrode formed of the
conductive layer on the first surface, where the second
discontinuous electrode includes a plurality of second concentric
electrode portions coupled to a second electrode connection and
includes a break in each electrode portion of the plurality of
second concentric electrode portions. In such embodiments, the
first concentric electrode portions and the second concentric
electrode portions are arranged in alternating concentric
structures such that each first concentric electrode portion of the
first concentric electrode portions is adjacent a second concentric
electrode portion of the second concentric electrode portions.
[0151] According to an embodiment, a MEMS device with a deflectable
structure includes a first structure and a second structure, where
the first structure is spaced apart from the second structure and
the first structure and the second structure are configured to vary
a distance between portions of the first structure and the second
structure during deflections of the deflectable structure. In such
embodiments, the first structure includes a first electrode
configured to have a first charge polarity and a second electrode
configured to have a second charge polarity, where the second
charge polarity is different from the first charge polarity. The
second structure includes a third electrode configured to have the
first charge polarity. Other embodiments include corresponding
systems and apparatus, each configured to perform corresponding
embodiment methods.
[0152] Implementations may include one or more of the following
features. In various embodiments, the first structure includes the
deflectable structure and the second structure includes a rigid
structure. In some embodiments, the MEMS device is an acoustic
transducer, the deflectable structure includes a deflectable
membrane, and the rigid structure includes a rigid perforated
backplate. In further embodiments, the first structure includes a
rigid structure and the second structure includes the deflectable
structure. In particular embodiments, the MEMS device is an
acoustic transducer, the rigid structure includes a rigid
perforated backplate, and the deflectable structure includes a
deflectable membrane.
[0153] According to an embodiment, a method of forming a MEMS
device includes forming a first structure, forming a structural
layer in contact with the first structure around a circumference of
the first structure, and forming a second structure. The first
structure includes a dipole electrode including a first electrode
and a second electrode. The second structure includes a third
electrode. In such embodiments, the structural layer is in contact
with the second structure around a circumference of the second
structure and the first structure is spaced apart from the second
structure by the structural layer. Other embodiments include
corresponding systems and apparatus, each configured to perform
corresponding embodiment methods.
[0154] Implementations may include one or more of the following
features. In various embodiments, forming the first structure
includes forming a first structural layer, forming a plurality of
first electrodes on a top surface of the first structural layer,
and forming a plurality of second electrodes on a bottom surface of
the first structural layer. In some embodiments, forming the first
structural layer includes forming a first insulating layer. Forming
the first structural layer may include forming a first conducting
layer, forming a first insulating layer on a top surface of the
first conducting layer, and forming a second insulating layer on a
bottom surface of the first conducting layer.
[0155] In various embodiments, forming the first structure includes
forming a first structural layer, forming a plurality of first
electrodes on a first surface of the first structural layer, and
forming a plurality of second electrodes on the first surface of
the first structural layer. In some embodiments, forming the first
structural layer includes forming a first conducting layer and
forming a first insulating layer between the first conducting layer
and both the plurality of first electrodes and the plurality of
second electrodes. In particular embodiments, the plurality of
first electrodes and the plurality of second electrodes are formed
on and in contact with first insulating layer. The plurality of
second electrodes may be formed overlying the plurality of first
electrodes, and forming the first structure may further include
forming a second insulating layer between the plurality of first
electrodes and the plurality of second electrodes.
[0156] According to various embodiments described herein, an
advantage may include MEMS transducers having movable electrodes
with low risk of collapse, i.e., pull-in, for the electrodes due to
embodiment multi-electrode configurations described herein.
[0157] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons skilled
in the art upon reference to the description. It is therefore
intended that the appended claims encompass any such modifications
or embodiments.
* * * * *